NIF optical materials and fabrication technologies: an overview

Abstract

The high-energy/high-power section of the NIF laser system contains 7360 meter-scale optics. Advanced optical materials and fabrication technologies needed to manufacture the NIF optics have been developed and put into production at key vendor sites. Production rates are up to 20 times faster and per-optic costs 5 times lower than could be achieved prior to the NIF. In addition, the optics manufactured for NIF are better than specification giving laser performance better than the design. A suite of custom metrology tools have been designed, built and installed at the vendor sites to verify compliance with NIF optical specifications. A brief description of the NIF optical wavefront specifications for the glass and crystal optics is presented. The wavefront specifications span a continuous range of spatial scale-lengths from 10 µm to 0.5 m (full aperture). We have continued our multi-year research effort to improve the lifetime (i.e. damage resistance) of bulk optical materials, finished optical surfaces and multi-layer dielectric coatings. New methods for post-processing the completed optic to improve the damage resistance have been developed and made operational. This includes laser conditioning of coatings, glass surfaces and bulk KDP and DKDP and well as raster and full aperture defect mapping systems. Research on damage mechanisms continues to drive the development of even better optical materials.

Dynamic Accuracy Design Method of Ultra-precision Machine Tool

“…Therefore, the frequency domain errors in the KDP machining must be controlled. Table 1 lists the specifications for KDP crystal machining in ICF [23]. GRMS, Rq, pk, avg and PSD represent RMS gradient, RMS roughness, peak value, mean value and power spectral density, respectively.…”

Laser induced damage due to scratches in the surface of nonlinear optical crystals KH2PO4 (KDP)

“…As frequency converters, potassium dihydrogen phosphate, KDP (KH 2 PO 4 ), is frequently employed in large aperture laser systems because KDP is a kind of nonlinear optical material that can grow to very large dimensions [1][2][3]. Owing to its deliquescence, KDP is mostly finished by virtue of diamond cutting/turning under dry conditions or using cutting oil [4,5].…”

The National Ignition Facility: the world's largest optical system

“…Some of the more significant changes between NIF and Nova, the preceding fusion laser at LLNL, are rapid growth for KDP and large-aperture conventional growth of DKDP crystals, continuous pour technology of a reformulated laser glass, deterministic grinding and finishing technologies, deterministic coating deposition processes, deformable mirrors, and finally laser processing of all high fluence optics. 6 …”